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<script>
    /**
     * 堆 Heap
     * 
     * 栈 Stack
     * ----》都是从电脑内存条中分配出来的内存
     * 上下文 EC [execution context] 执行上下文
     * GO G Object
     * VO/AO V  A
     */
    {
        var a = { n: 10 };
        var b = a;
        console.log('a',a);
        console.log('b',b);
        a.x = a = { n: 20 }
        console.log('a2',a);
        console.log(a.x);//nudefinde
        console.log(b);//{n:10,x:{n:20}}
    }
</script>